U.S. patent number 5,850,836 [Application Number 08/532,391] was granted by the patent office on 1998-12-22 for morphometric x-ray absorptiometry (mxa).
This patent grant is currently assigned to Hologic, Inc.. Invention is credited to Peter Steiger, Howard P. Weiss.
United States Patent |
5,850,836 |
Steiger , et al. |
* December 22, 1998 |
Morphometric x-ray absorptiometry (MXA)
Abstract
MXA Scan analysis in accordance with an exemplary embodiment of
the invention can be viewed as a process of placing points on the
lateral morphometry image at the anterior, mid, and posterior
positions of the inferior and superior endpoints for each vertebral
body in the spinal region of interest. These point locations are
then used to calculate the anterior, mid, and posterior heights of
the vertebral bodies. These heights are then compared to one
another and to known normal values for the heights and ratios of
the heights for each vertebral body and among vertebral bodies to
quantify the degree of vertebral deformity.
Inventors: |
Steiger; Peter (Framingham,
MA), Weiss; Howard P. (Newton, MA) |
Assignee: |
Hologic, Inc. (Waltham,
MA)
|
[*] Notice: |
The portion of the term of this patent
subsequent to January 3, 2014 has been disclaimed. |
Family
ID: |
24121589 |
Appl.
No.: |
08/532,391 |
Filed: |
September 22, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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176418 |
Jan 3, 1998 |
5483960 |
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Current U.S.
Class: |
600/300; 382/132;
378/54; 128/922 |
Current CPC
Class: |
A61B
6/4441 (20130101); A61B 6/505 (20130101); A61B
6/482 (20130101); Y10S 128/922 (20130101) |
Current International
Class: |
A61B
6/00 (20060101); A61B 006/00 () |
Field of
Search: |
;128/653.1,920,922
;378/54-56,196,901 ;364/413.13,413.22,413.23,413.26 ;382/132 |
References Cited
[Referenced By]
U.S. Patent Documents
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4903203 |
February 1990 |
Yamashita et al. |
5483960 |
January 1996 |
Steiger et al. |
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Other References
W Kalender, H. Brestowski, and D. Felsenberg, "Bone Mineral
Measurement: Automated Determination of Midvertebral CT Section",
Radiology, vol. 168, pp. 219-221, 1988. .
J.A. Stein, "Technological Advances in Bone Densitometry, 8th Int'l
Symposium on Bone Structure", Function & Disease, Apr. 1990.
.
W.A. Kalender and H. Eidloth, "Determination of Geometric
Parameters and Osteoporosis Indices for Lumbar Vertebrae from
Lateral QCT Localizer Radiographs", Osteoporosis International,
vol. 1, No. 3, pp. 197, Jun. 1991. .
L. Kalidis, et al., Morphometric Analysis Of Digitized Radiographs:
Description Of Automatic Evaluation, Current Research in
Osteoporosis and Bone Mineral Measurement II: 1992, printed in
Proceedings of the Third Bath Conference on Osteoporosis and Bone
Measurement, Bath, England, pp. 14-16, Jun. 1992. .
"Bath Conference on Osteoporosis and Bone Mineral", Lunar News, pp.
9-10, Sep., 1992. .
Willi A. Kalender. Copies of Slides presented at the 8th
International Workshop on Bone Desitometry, Bad Reichenhall,
Germany, pp. 10-11, Apr. 28, 1991 -May 2, 1991. .
"Abstracts-8th International Workshop on Bone Densitometry: Apr. 28
-May 2, 1991, Bad Reichenhall, Germany", Osteoporosis
International, vol. 1, No. 3, Jun. 1991..
|
Primary Examiner: Smith; Ruth S.
Attorney, Agent or Firm: Cooper & Dunham LLP
Parent Case Text
This is a continuation of application Ser. No. 08/176,418 filed
Jan. 3, 1994. Now U.S. Pat. No. 5,483,960.
Claims
We claim:
1. A method for vertebral morphometry comprising the steps of:
obtaining paired AP (anterior/posterior or posterior/anterior)
centerline and lateral morphometry images of a patient covering at
least the T4 (thoracic 4 ) through L4 (lumbar 4 ) vertebrae by
using radiation to carry out an AP scan and a lateral scan without
moving the patient between the scans, wherein said AP scan is
carried out first to produce an AP image which is analyzed to
determine the centerline of the patient's vertebral column and said
centerline is used to maintain a constant distance between the
centerline and an origin of the radiation while carrying out the
lateral scan;
displaying the paired AP image and the lateral image side-by-side
together with a pair of spatially synchronized cursors pointing to
anatomically corresponding current locations on both images to help
identify vertebrae and visualize spatial relationships of anatomy
and pathology between said AP and lateral images which are
displayed side-by-side;
designating six points for each vertebra with said cursor;
calculating posterior, mid- and anterior vertebral heights and
vertebral wedge indices with the use of points designated in the
designating step; and
displaying calculated heights and indices characterizing the
patient.
2. A method for vertebral morphometry as in claim 1, wherein the
radiation comprises a fan beam and in which the step of obtaining
said images comprises maintaining during said lateral scan an
orientation of the fan beam in which one of the boundaries of the
fan beam is horizontal.
3. A method for vertebral morphetry comprising the steps of:
imaging a patient to obtain paired vertebral AP (anterior/posterior
or posterior/anterior) and lateral scans, at least one of said AP
and lateral scans being obtained by imaging the patient with
penetrating radiation energy; and
utilizing said paired scans to carry out computer-assisted
vertebral morphometric analysis comprising manual designation by an
operator of the locations of at least a plurality of
morphometrically significant points on a lateral image resulting
from said lateral scan.
4. A morphometric method comprising the steps of:
imaging a patient to obtain paired AP (anterior/posterior or
posterior/anterior) and lateral scan images, at least one of said
paired images being obtained with penetrating radiation energy;
and
utilizing said paired images to determine a curve connecting
anterior points of the lateral vertebral image and to derive a
Kyphosis index related to the ratio of a deviation of the thoracic
curve from a line connecting the lower anterior point of vertebrae
T4 (thoracic 4 ) and L4 (lumbar 4 ) and the distance from the lower
anterior point of vertebra T4 and the intersection of the curve
with a polynomial fit.
5. A system for vertebral morphometry comprising:
a bone densitometer imaging a patient to obtain paired AP
(anterior/posterior or posterior/anterior) and lateral scan
vertebral images, at least one of the paired images being obtained
with penetrating radiation energy;
a display for side-by-side display of said images showing spatially
synchronized movable cursors pointing at all times at anatomically
corresponding portions of the AP and lateral images to help
identify vertebrae and to help visualize spatial relationships of
anatomy and pathology between said AP and lateral images which are
displayed side-by-side; and
a processor coupled with the display and responsive to the
designation of points on the lateral image, including the manual
designation and/or confirmation of points by an operator, to carry
out vertebral morphometric analysis.
6. A vertebral morphometry method comprising the steps of:
imaging a patient with penetrating radiation to obtain paired
vertebral AP (anterior/posterior or posterior/anterior) and lateral
scan images;
displaying said images side-by-side together with a pair of
spatially synchronized cursors pointing to respective spatially
corresponding points on said AP and lateral images to help identify
vertebrae and visualize said spatial relationships of anatomy and
pathology between said AP and lateral images which are displayed
side-by-side;
utilizing the displayed images and said synchronized cursors to
carry out computer-assisted vertebral morphometric analysis by
placing markers on predetermined points on said displayed images to
mark predetermined points on one or more of the vertebral, wherein
the markers are initially placed by computer-assisted suggestion
based on knowledge of vertebral anatomy.
7. A vertebral morphometry method as recited in claim 6, wherein
each vertebral body forming the vertebrae is described by its own
coordinate system.
8. A vertebral morphometry method as recited in claim 7, wherein
each coordinate system is determined by a predetermined point of
each vertebra.
9. A vertebral morphometry method as recited in claim 8, wherein
each predetermined point is the inferior anterior point of each
vertebra.
10. A vertebral morphometry method as recited in claim 9, wherein a
polynomial fit is made through each predetermined point.
11. A vertebral morphometry method as recited in claim 10, wherein
the polynomial fit is a fourth degree polynomial fit.
12. A vertebral morphometry method as recited in claim 6, wherein
one of the images displayed side-by-side can be scrolled while the
other image remains fixed.
13. A vertebral morphometry method as recited in claim 6, wherein
the computer-assisted suggestions for marker placement are based on
knowledge of normal vertebral anatomy.
14. A vertebral morphometry method as recited in claim 6, wherein
the computer-assisted suggestions for marker placement are based on
prior knowledge of vertebral anatomy of the same patient.
15. A vertebral morphometry method as recited in claim 6, further
comprising a step of determining heights of various sections of
each vertebral body using the placed markers.
Description
REFERENCE TO MICROFICHE APPENDIX
The present application incorporates a microfiche appendix with two
sheets of of microfiche having 153 frames (see parent U.S. Pat. No.
5,483,960).
BACKGROUND OF THE INVENTION
The invention is in the field of imaging using penetrating
radiation and pertains in particular to obtaining and processing
penetrating radiation measurements and especially to morphometric
x-ray absorptiometry referred to by the acronym MXA.
In fields such as the diagnosis of osteoporosis, it can be
desirable to confirm a fracture associated with low bone material
density, such as a hip, wrist or vertebral fracture. For example,
see Seeley D. G., Browner W. S., Nevitt M. C., Genant H. K., Scott
J. C., Cummings S. R.: Which fractures are osteoporotic? Third
International Symposium on Osteoporosis, Copenhagen, Denmark;
Osteopress ApS, Copenhagen, 1990; Vol. 2, pp 463-464. Lateral
thoratic and lumbar spine films have been utilized for the
diagnosis of vertebral fractures in order to confirm crush and
wedge deformities of vertebral bodies in the range encompassing T4
and L4 vertebrae. A number of studies have evaluated methods for
the identification of vertebral fractures by vertebral morphometry
and the correlation thereof with readings of radiologists. For
example, see A) Hedlund L. R., Gallagher J. C.: Vertebral
morphometry in diagnosis of spinal fractures, Bone Miner 1988; 5:
59-67, B) Hedlund L. R., Gallagher J. C., Meeger C., Calcif Tissue
Int 1989; 44: 168-172, c) Davies K. M., Recker R. R., Heaney R. P.:
Normal vertibral dimensions and normal variation in serial
measurements of vertabras, J Bone Min Res 1998; 4: 341-349 D)
Smith-Bindman R., Steiger P., Cummings S. R., Genant H. K.: The
index of Radiographic Area (IRA): a new approach to estimating the
severity of vertebral deformity. Bone Miner 1991; 15;137-150. E)
Smith-Bindman R., Cummings S. R., Steiger P., Genant H. K.: A
comparison of morphometric definitions of vertebral fracture, J
Bone Min Res 1991; 6: 25-34, F) Minne H. W., Leidig G., Wuster C.
H. R., et al: A newly developed spine deformity index (SDI) to
quantitate vertebral crush fractures in patients with cateoporosis,
Bone Mineral 1988; 3: 335-349, G) Sauer P., Leidig G., Minne H. W.,
Duckeck G., Schwarz W., Siromachkostov L., Ziegler R.: spine
deformity index (SDI) versus other objective procedures of
vertebral fracture identification in patients with osteoporosis: a
comparative study, J Bone Min Res 1991; 6(3): 227-338, H) Eastell
R., Cedel S. L., Wahner N.W., Riggs B. L., Melton L. H.:
Classification of vertebral fractures. J Bone Min Res 1991; 6(3):
207-215. Stoner S: Change in vertebral shape in spinal
osteoporosis, Some vertebral morphometry techniques involve
digitizing conventional radiograms (x-ray films) and obtaining
anterior, posterior and mid-vertebral heights. However, there can
be disadvantages in this approach such as operator imprecision in
placing the points for digitization on the radiograms, the use of
multiple exposures to image both thoracic and lumbar regions of the
spine due to the relatively large attenuation difference between
the thoracic and lumbar areas, the possible need for retakes, and
the radiation dose that can be associated with this procedure (such
as 900 mRem without repeat exposures). In addition, geometric
distortion can be a factor in using such digitized conventional
x-ray films because they typically are obtained using cone beam
geometry. As a result of such geometric distortion, different
points in the radiogram are magnified and distorted in relative
position in different ways. For example, areas closer to the edge
of the film image are magnified more and are viewed at a somewhat
oblique angle, whereas areas close to the center are magnified less
and are viewed at an angle closer to perpendicular. Still in
addition, the identification of vertebral levels can be difficult
and film handling and archiving can involve considerable overhead.
Rectilinear scanning, using a bone densitometer with a thin pencil
beam of x-rays can counter the geometric distortion problem but can
introduce the disadvantage of a much longer scanning time to
acquire the necessary x-ray data. The use of a fan beam CT scanner
in a scout view mode can decrease the scanning time as compared
with rectilinear scanning. See W. A. Kalender, et al.,
Determination of Geometric Parameters and Osteoporosis Indices for
Lumbar Vertebrae from Lateral QCT Localizer Radiographs, 8th
International Workshop on Bone Densitometry, Bad Reichenhall,
Germany, Apr. 28-May 2, 1991. However, it is believed that the
proposed CT images were not dual energy images and that the
proposal may not completely address the issues of geometric
distortions and/or vertebral magnification factor differences as
between the AP and lateral images. Moreover, it is believed that
QCT (quantitative computerized tomography) so used in morphometry
typically images a relatively limited region of the spine such as
the T12 through L4 vertebrae.
When bone densitometry equipment is used to obtain penetrating
radiation images useful in morphometry, typically a patient is
placed on a table and remains stationary while a radiation source
moves relative to the patient position. A radiation detector is
positioned on the opposite side of the table from the source to
detect radiation transmitted through the patient. The radiation
source and detector are usually mechanically linked by a structure
such as a C-arm to ensure alignment between them. Both x-ray tubes
and isotopes have been used as a source of the radiation. In each
case, the radiation from the source is collimated to a specific
beam shape prior to reaching the patient to thereby restrict the
radiation field to the predetermined region of the patient opposite
which are located the detectors. In the case of using x-rays,
various beam shapes have been used in practice or proposed,
including fan beam, pencil beam and cone or pyramid beam
shapes.
Bone densitometry systems are manufactured by the assignee hereof
under tradenames including QDR 2000plus, QDR-2000, QDR-1500,
QDR-1000plus, QDR-1000W and QDR-1000. Certain information
respecting such equipment can be found in brochures originating
with the assignee hereof and identified by the designators B-108
(September 1993 ) USA, B-109 (September 1993 ) USA, S-117
(September 1993 ) USA and S-118 (October 1993 ) USA. Commonly owned
U.S. Patents pertaining to such systems include U.S. Pat. Nos.
4,811,373, 4,947,414, 4,953,189, 5,040,199, 5,044,002; 5,054,048,
5,067,144, 5,070,519, 5,132,995 and 5,148,455 as well as U.S. Pat.
Nos. 4,986,273 and 5,165,410 (assigned on its face to Medical &
Scientific Enterprises, Inc. but now commonly owned). Commonly
owned U.S. Patents application Ser. No. 08/156,287 filed on Nov.
22, 1993 also pertains to a bone densitometer. Said Patents and
application and said brochures are hereby incorporated by reference
herein. Other bone densitometry systems are believed to be offered
by other companies, such as the Lunar Corporation of Madison, Wis.
See, e.g., J. Hanson, et al., New Imaging Bone Densitometer,
Presented at: The American Society for Bone and Mineral Research
15th Annual Meeting, 18-22 Sep. 1993, Tampa, Fla., USA, an undated
flier entitled Product Information EXPERT, and U.S. Pat. No.
5,228,068, none of which is necessarily admitted to be prior art
against the invention claimed in herein. Note the discussion of an
approach to morphometry in said U.S. Pat. No. 5,228,068.
For a general background concerning MXA, see Morphometric X-Ray
Absorptiometry (MXA), a document prepared by the assignee hereof
and identified by the designation W-126 (October 1993 ) USA, which
is hereby incorporated by reference. Other articles of interest
include A) Cummings S R, Black D M, Nevitt M C, Browner W S, Cauley
J A, Genant H K, Mascioli S R, Scott J C, Seeley D G, Steiger P,
Vogt T M: Appendicular bone density and age predict hip fracture in
women, JAMA 1990; 263(5): 665-668, B) Kleerekoper M, Parfitt A M,
Ellis B I: Measurement of vertebral fracture rates in osteoporosis.
Osteoporosis: Procedings of the Copenhagen Symposium on
Osteoporosis Jun. 3-8, 1984. Christiansen, Arnaud, Nordin and et
al. ed. 1994 Department of Clinical Chemistry, Glostrup Hospital.
Denmark, C) Leidig G, Storm T, Genant HK, Minne HW, Sauer P,
Duckeck G, Siromachkostov L, Sorensen CH, Ziegler R: Comparison of
two methods to assess vertebral fractures. Third Int Symposium on
Osteoporosis, Copenhagen, Denmark; Osteopress ApS, Copenhagen,
Denmark, 1991; Vol 2, pp 626-628, D0 Ettinger B, Black DM, Nevitt
MC, Rundle AC, Cauley JA, Cummings SR, Genant HK: Contribution of
vertebral deformities to chronic back pain and disability, J Bone
Miner Res 1992; 7(4): 449-456.
Summary of the Invention
A vertebral morphometry process in accordance with a non-limiting
example of the invention estimates vertebral body dimensional
parameters to quantify vertebral deformities. For a morphometry
examination in accordance with the invention, typically two scans
are performed such as an AP centerline scan to determine spine
alignment and a lateral morphometry scan for morphometric analysis.
The centerline scan is an AP scan similar to that acquired in
AP/Lateral scanning; however, whereas a typical centerline scan
used for bone densitometry purposes may image a spinal region that
is about 6 inches long, a typical centerline AP scan for
morphometry in accordance with the invention can image a spinal
region which in the range of 20 inches long. Similarly, the second
morphometry scan, e.g., a lateral scan which images a spinal region
which also can be in the range of about 20 inches in length. Both
scans can include all thoracic and lumbar vertebrae, or a subset
thereof such as thoracic vertebrae T4-T12 and lumbar vertebrae
L1-L4.
Morphometry scans are analyzed in accordance with an example of the
invention by defining the positions of three reference points,
anterior, posterior, and mid, on each of the two endplates,
superior and inferior, of each vertebral body. For a baseline
morphometry scan, the centerline and morphometry scans are
displayed side-by-side. The system can suggest point placements
based upon its pre-stored knowledge of normal vertebral anatomy.
Each vertebral body is described by its own coordinate system
determined by the inferior anterior point of each vertebra and by a
high-degree polynomial, such as a fourth degree polynomial, made to
fit through those points. This is designed to reduce
operator-induced variation and to accelerate image evaluation. An
operator can change the suggested point positions by adjusting the
positions on each displayed vertebral body of three markers on each
endplate in ascending order. A second position cursor automatically
tracks the position of the active reference point on the AP
centerline scan. For each vertebral body analyzed, a Vertebral
Dimensions Report can be created to provide estimates for: (a)
posterior height, which is the distance between the posterior
points on the superior and inferior endplates of the specific
vertebral body; (b) mid height, which is the distance between the
mid points on the superior and inferior endplates of the specific
vertebral body; (c) anterior height, which is the distance between
the anterior points on the superior and inferior endplates of that
specific vertebral body; (d) wedge parameter, which is the ratio of
the anterior height to the posterior height of that specific
vertebral body; and (e) mwedge parameter, which is the ratio of the
mid height to the posterior height of that specific vertebral body.
In addition, during analysis of a follow-up morphometric scan using
a "compare" feature, the follow-up morphometry scan can be
displayed beside the baseline morphometry scan image. The vertebral
endplate markers from the baseline scan analysis can transfer
automatically onto the follow-up scan and move as a group to help
position the markers as a group on the morphometry scan. Then,
individual markers can be adjusted if necessary.
In broader terms, the invention is embodied in a method and a
system which image a patient with dual energy penetrating radiation
to obtain paired vertebral AP and lateral scan images and utilize
the paired images to carry out computer-assisted vertebral
morphometric analysis. In the course of the lateral scan, a
constant vertebral magnification factor is maintained despite the
fact that the vertebral centerline projection on a horizontal plane
may curve or skew. In addition, the same vertebral magnification
factor can be maintained for each of the AP and lateral scans.
Still in addition, the same magnification factor can be maintained
as between an initial examination and a later, follow up
examination of the same patient. Stated differently, in accordance
with one aspect of the invention a constant vertebral magnification
factor can be maintained for all examinations of all patients, as
well as within each examination, in order to ensure better fit of
examination results to each other and to a knowledge database. Such
constant vertebral magnification factor can be achieved by
maintaining a constant distance between the source of the
penetrating radiation and a vertebral centerline. The AP scan can
be taken within a relatively short time interval, such as less than
a minute (e.g., 25 seconds) while the lateral scan can take much
longer, such as more than a minute (e.g., 10 minutes). If the AP
scan will be used for bone mineral density analysis in addition to
its use for morphometry in accordance with the invention, the AP
scan also can take several minutes, e.g., 6 minutes. For the
lateral scan, the fan beam of penetrating radiation can maintain an
orientation in which one of the boundaries of the fan is
substantially horizontal (and parallel to the patient bed surface).
In addition to the parameters referred to above, the morphometry
according to the invention can derive estimates of Kyphosis,
Lordosis and Scoliosis parameters.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the invention may be obtained from
the following description when taken in conjunction with the
drawings, in which:
FIGS. 1A and 1B illustrate a side-by-side display of paired lateral
and AP vertebral images obtained and displayed in accordance with
an embodiment of the invention for use in computer-assisted
vertebral morphometry in accordance with the invention.
FIG. 1C illustrates a local coordinate system used for each
vertebra in accordance with an embodiment of the invention.
FIG. 2 illustrates a patient positioned for centerline
AP/morphometry scans.
FIGS. 3A and 3B illustrate a display of an enlarged lateral image
and a corresponding AP image, respectively.
FIG. 4 illustrates the orientation of a fan beam of x-rays for a
lateral scan.
FIG. 5 illustrates a procedure for placing markers on a lateral
vertebral image.
FIGS. 6A and 6B illustrate an enlarged lateral image and an AP
image, respectively, with corresponding synchronized markers or
cursors thereon.
FIG. 7 illustrates a vertebral dimensions report.
FIG. 8 illustrates morphometry summary analysis report.
FIG. 9 illustrates a vertebral deformity report.
FIG. 10 illustrates a spinal deformity report.
FIGS. 11A and FIG. 11B illustrates analysis of a follow-up
morphometry scan.
FIG. 12 is a perspective view illustrating an alternative bone
densitometry system useful in practicing the invention.
FIG. 13 is a sectional view illustrating the system of FIG. 12 when
used for an AP scan.
FIG. 14 is a sectional view similar to that of FIG. 13 but
illustrating the system when used for a lateral scan.
FIG. 15 is a block diagram illustrating functional components of a
system useful in carrying out an embodiment of the invention.
FIG. 16 illustrates the measurement of a Kyphosis factor.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIGS. 1A and 1B illustrate a side-by-side display of a spinal
lateral image on the left and a spinal AP image on the right,
respectively, obtained with the previously identified QDR-2000
series bone densitometry system available from the common assignee.
For morphometry purposes, the operation of the commercially
available system is modified under the control of morphometry
software operating in accordance with the invention, in conjunction
with the commercially available control software for the systems
installed in this country, which is hereby incorporated by
reference. The morphometry software is provided as a microfiche
appendix.
To obtain paired AP and lateral images of the type illustrated in
FIG. 1A and FIG. 1B the bone densitometry system first carries out
an AP scan, modified in accordance with the invention to cover a
longer region of the spine, to obtain the AP image shown in FIG.
1B. This image is obtained by scanning a supine patient, for
example a patient in the position illustrated in FIG. 2, with a fan
beam of x-rays oriented such that the central axis of the x-ray
beam is vertical. A procedure for obtaining the paired scans and
processing them is described in pages G1-34 of the QDR-2000
Operator's manual and User's Guide supplied by Hologic, Inc. of
Waltham, Mass., Document No. 080-0384 Revision E, which pages are
herby incorporated by reference. In the example illustrated in FIG.
2, the x-ray source is below the patient and the x-ray detectors
are above the patient, and the patient is centered on a table such
that the vertebral column centerline substantially coincides with
the central axis of the fan beam. The resulting image is still
called an AP (anterior-posterior) image in this specification,
although in this configuration it can be called more accurately a
PA (posterior-anterior) image. For the purposes of this invention,
no distinction is made between AP and PA images. Unless the AP
image is to be used for other purposes, such as for bone mineral
density analysis, it can be taken relatively quickly, such as over
a time of less than a minute (e.g., 25 seconds). The image
resolution therefore can be lower, but sufficient for morphometry
purposes in accordance with the invention, and the overall
examination time and patient dose can be thus reduced. The system
generates the AP image and carries out image processing which
includes an identification of a vertebral centerline and a start
position and a region of interest for the morphometry scan. A C-arm
which supports the x-ray source and detector is then pivoted while
the patient remains in the supine position such that, as
illustrated in FIG. 4, x-ray source 10 is at one side of patient 12
while x-ray detector 14 is at the other side, and such that one
boundary of fan-shaped x-ray beam 16 is horizontal and parallel to
the top surface of patient table 18. The line connecting the
lowermost detector element in x-ray detector 14 and the origin of
beam 16 is just above table 18, e.g., 1/8" to 1/4" above the table.
In this manner, geometric distortion can be suppressed and the
measured x-ray beam need not pass through table 18. The system then
carries out a lateral scan in which the distance between the origin
of beam 16 and the vertebral centerline is the same as for the AP
scan and, moreover, remains the same during the lateral scan even
if the projection of the centerline on a horizontal plane deviates
(within limits) from a straight line or from a line perpendicular
to the plane defined by the origin of beam 16 and detector elements
in x-ray detector 14. To maintain the distance between the beam
origin and the vertebral centerline constant, the source-detector
assembly can move along the source-detector axis during the lateral
scan, as controlled by the software controlling the morphometry
scan in accordance with the invention, depending on the position of
the vertebral centerline identified as a result of the AP scan.
After the lateral scan image is available, and is displayed
alongside the AP image as illustrated in FIG. 1A and FIG. 1B,
markers are placed on the endplates of each vertebral body, for
example in the spinal region including vertebrae T4-L4, on three
reference points (anterior, posterior, and mid) on each of the two
endplates (inferior and superior) of each vertebrae. The preferred
procedure for placing markers is: placement of Inferior Anterior
Points; adjustment of Inferior Posterior Points; adjustment of
Superior Anterior Point for L4; adjustment of Point Positions
Relative to Fit; and adjustment of Point Positions Relative to
Image. At each phase in this procedure, the system suggests point
placements based upon its knowledge of normal vertebral anatomy.
Each vertebral body is described by its own coordinate system
determined by the inferior anterior point of each vertebra, and a
fourth degree polynomial fit through those points is made. This is
designed to reduce operator-induced variation and to accelerate
image evaluation. A dual windowing feature in the system allows the
operator to scroll the (the lateral image) in FIG. 1A up or down
while the right image (the AP) remains fixed and shows the entire
spinal region which was imaged in the AP scan. Such scrolling is
illustrated in FIG. 3A and FIG. 3B. If while placing markers the
operator moves a marker off the screen (up or down), the system can
automatically scroll the display to show that portion of the spine.
In a preferred embodiment of the invention, an active marker is
displayed as a blue circle on the image in FIG. 1A. The position,
on the spine, of the active marker is denoted on the image in FIG.
1B by a blue dashed line which moves along the AP image in
synchronism with any movement of the marker on the image in FIG.
1B, in order to ensure that the markers on the two images shown in
FIG. 1A and FIG. 1B, respectively, track each other in position at
all times. Markers are placed sequentially, as indicated in FIG. 5,
beginning with the anterior marker on the inferior endplate of the
lowest vertebra of interest, in this case L4. The operator observes
the markings which are already placed on the image (lateral) in
FIG. 1A by the system derived from on a knowledge database of
typical vertebral anatomy. The operator moves the first marker,
using arrow keys or a mouse that can be provided as a part of a
commercial QDR-2000 system, so that the marker is located as close
to the inferior endplate, and as far to the anterior, as possible
without going outside of the vertebral body. After the first marker
is positioned correctly, the operator presses an <Insert>
key, in response to which the system stores information defining
the position and identity of the point. The system automatically
changes the active marker to the next vertebral body, which the
operator similarly positions and enters. The system and the
operator continue up the spine until all markers for anterior point
positions, on the inferior endplate, are complete. The system
provides the location of the active point (vertebral body level)
and the active marker number. This is displayed under the
morphometry image at the far right as illustrated in FIG. 1A and
FIG. 1B (See also FIG. 6A and FIG. 6B). The first two characters
provide the location on the spine (specific vertebral body), and
the last number indicates the active marker. A similar procedure
adjusts the inferior posterior point positions. Points are adjusted
beginning with the posterior marker on the inferior endplate of L4
in this example. Similarly, the superior anterior point positions
are adjusted. A group of points can be moved with respect to the
curve of the spine. When the points are positioned correctly, a
report can be generated. Morphometry scan results can be reported
by different methods illustrated in FIGS. 7, 8, 9 and 10. A
Vertebral Dimensions Report (FIG. 7) shows the vertebral dimensions
in millimeters (mm). Anterior (AH), mid- (MH) and posterior (PH)
vertebral heights are listed. Anterior/posterior height ratios
(WEDGE) and mid/posterior (MWEDGE) height ratios are also provided.
A Morphometry Summary Analysis Report (FIG. 8) shows the
calculations (only) from each of the other report screens. Since
all of the calculations appear on one page, this report can provide
a convenient presentation of the information. A Vertebral Deformity
Report (FIG. 9) labels vertebral deformities according to an
algorithm proposed, e.g., by McCloskey et al. (McCloskey E. V.,
Spector T. D., Eyres K. S., O'Rourke N., Fern D. E., Kanis J. A.
1993 Assessment of vertebral deformity--validation of a new method
with high specificity. Osteoporosis Int 3(3): 138-147). Anterior,
central, posterior and crush deformities are evaluated separately.
The number of deformities is totaled per vertebra and per deformity
type. A Spinal Deformity Index Report shows the Spine Deformity
Index (SDI) as proposed, e.g., by Minne et al. (Minne H. W., Leidig
G., Wuster C. H. R., et al., 1988 A newly developed spine deformity
index (SDI) to quantify vertebral crush fractures in patients with
osteoporosis. Bone Mineral 3: 335-349). A number greater than 0
indicates a deformity, while a no entry indicates that a vertebra
is not considered significantly deformed. Indices are listed
separately for anterior (Ha), mid (Hm) and posterior (Hp) vertebral
heights. The indices are totaled per vertebra and per deformity
type. In accordance with another feature of the invention, a
Compare procedure can be used on follow-up scans to optimize marker
placements from one scan to another, and to save time. Since marker
positions, on a new scan of the same patient, are likely to be very
close to the prior scan, time can be save qd by automatically
matching-up the markers in accordance with the invention. The
Compare procedure comprises: Scan selection; Image adjustment;
Marker placement; and Report generation. The Scan Selection step is
the selection of a baseline scan for the comparison. The Image
Adjustment step comprises adjusting the contrast and brightness of
the displayed image, if necessary, to give the best definition to
the vertebral endplates. In the Marker Placement step, the current
(follow-up) morphometry scan appears on the left of the screen as
illustrated in FIG. 11A and the baseline scan appears on the right,
as illustrated in FIG. 11B. The system transfers the marker
positions from the baseline to the follow-up morphometry scan. The
operator can adjust the points on the image (the lateral image) in
FIG. 11A as a group to allow compensation for changes in spinal
curvature that may have occurred between the two scans due to
positioning changes or due to changes in patient anatomy. If the
shape of the vertebral bodies has changed, it may be easier to
reposition markers using the "Adjust Positions Relative to Image"
capability of the system after having used the "Adjust Positions
Relative to Fit" capability.
Stated in more formal terms, MXA Scan analysis in accordance with
an exemplary embodiment of the invention can be viewed as a process
of placing points on the lateral morphometry image at the anterior,
mid, and posterior positions of the inferior and superior endpoints
for each vertebral body in the spinal region of interest. These
point locations are then used to calculate the anterior, mid, and
posterior heights of the vertebral bodies. These heights are then
compared to one another and to known normal values for the heights
and ratios of the heights for each vertebral body and among
vertebral bodies to quantify the degree of vertebral deformity.
MXA Scan analysis in accordance with the invention can follow an
algorithm which is a knowledge based and semi-automatic procedure
for placing the required points. For baseline scans (no previous
analyzed scan for the patient), the algorithm can use prior
knowledge of relationships between vertebral heights based on
published literature and on analysis of morphometric measurements
previously carried out in accordance with the invention for other
patients and selected in accordance with objective and/or
subjective criteria for inclusion in the knowledge database. As
information is supplied for a given patient, the algorithm
incorporates that information to adjust the proposed placement of
the points. For FollowUp scans, the previous scan results are used
as the initial guess for the placement of points and modified to
compensate for changes in patient positioning and/or possible
deformity of the vertebral bodies. Points are placed either by
moving a cursor via directional commands entered on the computer
keyboard or by manipulation of the positions via a pointing device
such as a mouse. The algorithm is substantially the same regardless
of which implementation is used, except as noted below.
The following steps are followed for Baseline Scans in accordance
with a non-limiting example of the invention. Note that an example
of the software controlling the process is set forth in the
microfiche appendix:
1. An operator of the system places (preferably with a mouse) one
point per vertebra starting at L4 and extending 1 vertebra beyond
the topmost vertebra to be quantified. The points should follow the
outline of anterior edges and should be placed at the inferior
anterior edge of the endplates. This generates a set of I anterior
points A.sub.1 -A.sub.I, where A.sub.i is defined by coordinates
(X.sub.ai , Y.sub.ai). If the mouse is not being used, then the
algorithm guesses at the point position for the next vertebra based
on the position(s) of the points on the inferior vertebrae.
2. A 4th degree polynomial is fit through A.sub.1 -A.sub.I :
Note that x (posterior/anterior axis) is fit as a function of y
(caudal to cranial axis).
3. For each vertebral body, a local coordinate system is defined
with the inferior anterior point of the vertebral body as the
origin and the perpendicular to the fit as the local y axis, as
illustrated in FIG. 1C:
4. The process generates a set of inferior posterior points for the
specified vertebral bodies. The points are initially positioned
relative to the respective local coordinate system for each
vertebral body at a distance from the inferior anterior point
proportional to the distance between the inferior posterior point
and inferior anterior point on the lowest vertebral body. The ratio
of these distances can be maintained in the knowledge base which
guides the process. The operator then adjusts the positions of the
inferior posterior points for the respective vertebrae. As a point
is adjusted, similar adjustments are made automatically to inferior
posterior points on superior vertebral bodies preserving the angle
between local y axis and a line connecting the inferior posterior
and anterior points and the ratio of the distances between the
inferior posterior and anterior points.
5. The process generates a single superior posterior point at a
predefined distance along the 4th order fit. The operator then
adjusts the location of this point.
6. The process then generates the remaining points as follows:
a) Superior anterior points are generated along the fit at
distances proportional to the distance between the inferior
anterior and superior anterior points on the lowest vertebral body.
The ratio of these distances is maintained in the knowledge base
which guides the process.
b) Superior posterior points are generated similarly as if the
anterior fit passed through the inferior posterior point. For the
lowest vertebra (usually but not necessarily L4), the posterior
height is calculated as a fixed proportion of the anterior height.
For the remaining vertebrae, superior posterior points are then
generated at distances proportional to the distance between the
inferior posterior and superior posterior points on the lowest
vertebral body. The ratios of these distances are maintained in the
knowledge base which guides the process.
c) Superior and Inferior midpoints are then generated. A point (l)
is calculated midway between the inferior posterior and anterior
points. A second point (u) is calculated midway between the
superior posterior and anterior points. The inferior and superior
midpoints are then located along a line connecting l and u such
that the distance between the inferior and superior midpoints
corresponds to data in the knowledge base. The inferior and
superior midpoints are offset equally from the points (l) and
(u).
7. The operator then adjusts the points as described below. Point
positions are stored at grid locations where the grid spacing is a
function of the data acquisition. All distances are expressed in
millimeters.
To adjust point positions after the points are placed as discussed
above, the process supplies three (3) modes of adjustment:
1) Selected points (relative to fit). The subset of points which
can be moved is a function of the currently selected cursor. Point
motion is performed relative to the fourth order polynomial fit in
the local coordinate system of each vertebral body as defined
above. The possible motions are summarized below for the different
candidate cursor positions:
a) Cursor at inferior anterior point. The fit is recalculated as
the inferior anterior point is moved. The positions of all points
on all vertebrae relative to their local coordinate system are
preserved.
b) Cursor at inferior posterior point. The angle and distance of
the inferior mid and superior anterior points are adjusted
corresponding to changes in the angle and distance of the inferior
posterior point relative to a coordinate system centered at the
inferior anterior point. The angle and distance of the superior
posterior and superior mid points are adjusted relative by a
similar amount by relative to the new position of the superior
anterior point (e.g., if the angle of the inferior posterior point
changes 10 degrees relative to the inferior anterior point, then
the angle of the superior posterior point changes 10 degrees
relative to the angle between the old superior posterior and
superior anterior points but calculated from the new superior
anterior point position).
c) Cursor at inferior mid point. The superior mid point is adjusted
relative to the current superior anterior point proportional to the
change in the position of the inferior midpoint relative to the
inferior anterior point.
d) Cursor at superior posterior point. The superior mid point is
adjusted relative to the current superior anterior point
proportional to the change in the position of the superior
posterior point relative to the superior anterior point e) Cursor
at superior anterior point. The superior mid and superior posterior
points are adjusted relative to the inferior anterior point
proportional to the change in the position of the superior anterior
point relative to the inferior anterior point.
f) Cursor at superior mid point. Only the superior mid point is
moved. In each case, point positions in vertebral bodies superior
to the current vertebral body are also adjusted. Motion is limited
so that no point can be moved outside the image frame.
2) Individual point. Only the specified point is moved. The point
to be moved is indicated by color and a cursor. The point position
may be changed via the keyboard or the mouse.
3) All points (relative to image). All the points may be moved. All
the points are marked in a color to indicate that they are
moveable. A specific point is indicated as a cursor although all
the points move as a group. Point positions may be changed via the
keyboard or the mouse. Motion is the same for all points. Motion is
limited such that no point can be moved outside the image
frame.
In baseline scans, the operator first performs type 1 adjustments
and then proceeds to move individual points, if necessary, using
type 2 adjustments. Type 3 adjustments are intended for Follow-Up
scans to compensate for overall shifts in general position
positioning.
In the case of follow-up scans, where morphometry in acccordance
with the invention has been carried out for the patient on a
previous occasion to obtain a Baseline Scan, a Follow-Up Scan
procedure is followed:
1. Baseline and follow-up scans are presented side-by-side. The
point positions from the previous (baseline) scan are reproduced on
the follow-up scan. The operator initially performs a type 3
repositioning (all points relative to image) to compensate for any
overall shift in patient positioning (or initial scan starting
position)
2. The operator then selects type 1 repositioning (relative to fit)
and adjusts the point positions to reflect differences in the
curvature of the spine. For the most part, the operator will need
to select and adjust specific inferior anterior positions to
reproduce the coordinate system for each vertebral body. In the
case of incident deformity, the operator should also adjust the
endplates by moving the inferior and superior posterior point
positions and possibly even correct the mid point placement (if
necessary).
3. If necessary, the operator can reposition individual points
using type 1 repositioning.
The results of the procedures described above can be used to
calculate and assess a number of additional parameters
characterizing a patient. For example, a Kyphosis index can be
calculated in accordance with the invention as illustrated in FIG.
16, by measuring the distance (l) between the lower anterior point
on T4 and the intersection of the spinal centerline with a straight
line from that point on T4 and the corresponding point on L4,
measuring the distance (h) from that line to the thoracic curve,
and multiplying the ratio (h/l) by the factor 100.
While the description above refers to using a QDR-2000 system to
obtain the AP and lateral images, in the alternative the system
described in said commonly owned patent application and illustrated
in FIGS. 12, 13 and 14 can be used. As illustrated in FIGS. 12-14,
a patient 1 lies horizontally (in a supine position) during
scanning on a table 2. X-ray radiation produced by an x-ray source
3 located beneath table 2 is transmitted through patient 1 to a
detector 4 having an array of detector positions and located above
patient 1. Both x-ray source 3 and detector 4 are supported on a
rigid arm 5 which maintains a selected source-to-detector distance
and alignment. In this example of the invention, x-ray source 3 has
a stationary anode. Adjacent x-ray source 3 is a slit collimator 6
made of a material an x-ray opaque material such as lead or
tungsten of sufficient thickness to substantially block x-rays from
source 3. One or more selectable slits have been machined into
collimator 6 to allow passage of the x-rays there-through. The
preferred embodiment includes a 1 mm wide collimator slit. The
x-ray radiation from the x-ray source 3 passes through the slit in
the collimator 6 and forms a fan shaped beam of x-rays 3a. The
angle subtended by beam 3a and the distance between its origin at
the focal spot of the x-ray tube and patient 1 are selected such
that beam 3a would not cover the entire cross-section of a typical
adult patient at any one time but would cover only a selected
portion of the width. In the preferred embodiment, fan beam 3a has
a maximum fan angle of 22 degrees. Of course, x-ray beam 3a not
only has width (along the X-axis illustrated in the Figures) but
also has a thickness along the Y-axis that is defined by the width
of the slit in collimator 6 and its distance from the origin of
beam 3a. A scan line is defined by the area of the patient
irradiated at any one time, i.e. the width and thickness of the
x-ray beam over which data is collected at one point in time. A
complete pass or scan consists of a set of adjacent scan lines
obtained over a period of time such that the entire region of
interest has been measured.
Opposite x-ray source 3 is detector 4 which in this embodiment
comprises approximately 200 detector elements arranged in a linear
configuration along the XZ plane which is about 16" long and is
about 42" from the origin of beam 3a (42" source-to-detector
spacing) and subtends a 22 degree fan angle. The detector elements
making up detector 4 are fixed with respect to x-ray source 3.
However, both x-ray source 3 and detector 4 can move with respect
to patient 1 and table 2. One motion translates fan beam 3a along
the patient axis defined by the spine, i.e., in the Y-direction.
Another motion rotates beam 3a around the patient. The center of
rotation is at a point C determined by the support arm 5 and the
method of rotation employed. In this embodiment, the detectors and
x-ray source are mounted to C-arm 5 which rotates on a set of
rollers 7. Thus, the center of rotation is determined by the outer
radius R of the C-arm, and is not at the origin (focal spot) of
beam 3a.
Table 2 can move horizontally along the X-axis as well as
vertically along the Z-axis. These motions can be carried out by
using a toothed-belt driven by a stepping motor or a DC servo
motor, although other implementations such as stepper-motor driven
lead-screws can also be employed. To perform a scan, a series of
scan lines of data must be acquired. To do this, C-arm 5 carrying
the x-ray source 3 and detector 4 is moved along the Y-axis along
the length of patient 1. This motion moves detector 4 and x-ray
source 3 to form a succession of spatially overlapping scan lines
adding up to a scanned rectangular area. The signals produced by
the detectors in response to x-rays impinging thereon at successive
scan lines are digitized by an analog to digital (A/D) converter
and are stored, for example on disk. A computer processes the
signals from the A/D converter into density representations and
images using the principles disclosed in the prior art discussed in
the background section of this disclosure.
For body structures of interest such as the spine, only a single
pass of fan beam 3a along the Y-axis is required because typically
the area of interest in the patient's body is covered by fan beam
3a as shown in FIGS. 13 and 14 for the Posteroanterior (PA) spine.
However, in order to reduce geometric distortion and improve
registration between lateral and PA views, in accordance with the
invention the system maintains a substantially constant distance
between x-ray source 3 and a centerline of the spine of patient 1.
To achieve this, a series of movements of C-arm 5 and table 2 are
required to ensure that the table and C-arm clear each other and to
ensure that the requisite source-spine distance is maintained. In
this embodiment, table 2 is moved along the X-axis and the Z-axis
appropriately while C-arm 5 is rotated about an Y-axis passing
through point C until the desired lateral position is reached.
FIG. 15 illustrates an embodiment in accordance with the invention
in block diagram form. Gantry 10 includes the structure illustrated
in FIGS. 12-14 as well as a suitable power supply for the x-ray
tube and the motors needed to move table 2 and C-arm 5 and to
operate collimator 6 in a manner similar to that in said QDR-2000
system. Detector 4 supplies x-ray measurements to A/D convertor and
preliminary processor 12 which carries out processing similar to
that carried out in said QDR-2000 system. The output of element 12
is supplied to a processor 14 which performs various calculations
and forms an image in a manner similar to that used in said
QDR-2000 system and, additionally, carries out morphometric
calculations. Data and images from processor 14 are supplied to a
console 16, display 18 and a recording device 20 for purposes and
in a manner similar to those in said QDR-2000 system. Two-way
arrows connect the elements of FIG. 15 to illustrate the fact that
two-way communication can take place therebetween. Conventional
elements have been omitted from the Figures and from this
description for the sake of conciseness.
For example, the illustrated equipment can be used as a first step
to derive a PA view of the patient's spine. The view can be in the
form of a processed image in digital form, or it can be in the form
of hard copy on x-ray film or on some other medium. The PA spine
image is analyzed to determine the center of the vertebral column,
and this information is used to maintain during a lateral scan the
same distance between the source and the spine centerline as during
the PA scan. For example, the each of the PA and lateral scans can
cover entire T4 to L4 range in a single scan at a source to
detector distance of 40 inches.
When both a PA view and a lateral view are available, selected
points on the vertebrae images can be marked, for example as
discussed in the articles by Smith-Bindman et al. discussed in the
Background of the Invention. For example, each vertebral body is
outlined by six points which can serve as the basis of the
calculation of posterior, mid- and anterior heights.
While a preferred embodiment of the invention has been described in
detail, it should be understood that changes and variations will be
apparent to those skilled in the art which are within the scope of
the invention recited in the appended claims.
* * * * *